In offshore pipe laying operations the pipe string between the lay barge and seafloor has to be kept taut to prevent overdue stress and buckling. The tension has to be maintained during all barge movements. For processing the pipe aboard the lay barge, the pipe string has to be kept steady, which means the pipe tension has to be kept within certain limits to compensate for the various sea conditions. The pipe string is squeezed between track loops or wheels which are propelled and controlled automatically.
From EP 0 296 272 A1 there is known a pipe tensioned machine for offshore pipe laying operations comprising squeeze elements for transferring tension forces to the pipes as well as a driving structure for the squeeze elements where two top squeeze and two bottom squeeze tracks are provided which may be moved relative to each other by an adjustment device mounted within a frame structure. Although this device operates properly it does not take account of the fact that due to the weight of the pipe more drive torque can be applied on the bottom tracks, and further, that the top of the machine is obstructed and no protrusions, like valve stems, in the pipe string can pass.
Other pipe tensioned machines (SAS Gouda by) use two opposing clamping tracks which are arranged either in horizontal or vertical direction. These machines squeeze, however, the cross section of the pipe string to an oval, which is due to the 180 degree opposed squeeze force.
A further four track type of tensioned machines (Remacut) is only suited for small pipe string diameters.
Therefore, there is a long felt and unmet need for a more effective pipe tensioned machine overcoming the before mentioned disadvantages and short comings which is adaptable to very different pipe diameters transmitting a controlled squeeze force on the pipe string.